This commit makes the core pass the sensitive keys to the platform
settings initialization, so that the platform settings implementation
can know which keys are sensitive keys during the initializing and do
the migration when needed.
This commit removes application library CLI/NCP dependency on platform
layer UART APIs. Instead, application layer provides callbacks sending
CLI/NCP data.
With this change, platforms with native support for formatted output
can simply implement the CLI output callback with something like
`vprintf()`.
jinran-google